The present invention relates to a technique of generating a synthesized image from multiple images that have been captured by cameras mounted on a vehicle, and more particularly relates to a technique effectively applicable to a monitoring system used as an safety check aid during vehicle driving.
A vehicle video monitoring system disclosed in Japanese Laid-Open Publication No. 11-78692 is one of the known systems for monitoring the surroundings of a running vehicle using cameras. In this system, a vehicle is equipped with multiple cameras, which are mounted here and there on the vehicle body to take a video of its surroundings. The respective images taken by these cameras are transformed and synthesized together while maintaining boundary continuity between them, thereby making a newly synthesized image and displaying it on the monitor screen.
A vehicle surrounding monitoring system of this type, however, will normally carry out the image processing on the supposition that each camera once mounted should be unable to change its position or the direction it faces. This is because it is practically impossible, or at least extremely difficult, to process multiple images for a synthesized image in real time with the continuously changing positions and directions of the cameras taken into account. The reason is that it takes too much time to perform that complicated processing and that the size and ability of such a system are limited.
On the other hand, considering the aerodynamics and design of a vehicle, it is highly probable that those cameras for use in such a monitoring system are mounted on various movable parts of the vehicle. For example, those cameras may be mounted around the rearview mirrors or on the trunk or hood of the vehicle.
Then, the following problems arise.
Specifically, when any of those movable parts, on which the camera is mounted, changes its state (e.g., moves), the image taken by that camera is affected by the change to possibly misalign the image that forms an integral part of the resultant synthesized image. For example, where a camera is mounted around an outside rearview mirror, the opening of a door with the mirror changes the direction the camera faces. As a result, only a portion of the synthesized image, corresponding to the image taken by the camera in question, misaligns, thus making the image on the screen unnatural to the viewer.
In addition, even if one of those cameras is mounted on a fixed part of the vehicle, a similar phenomenon is observed. For example, when a particular camera takes a video of an opening door, only a portion of the synthesized image, corresponding to the image taken by the camera, also misaligns. Such partial misalignment makes the synthesized image unnatural to the viewer and should be eliminated.